The invention relates to an electronic circuit for generating an output voltage having a defined temperature dependence.
In order to adjust signal transit times, use is frequently made in integrated circuits of time-delay circuits for the purpose of adjusting signals, such as clock signals, for example, to one another. The time-delay circuits serve the purpose, in particular, of making available at each point in the integrated circuits a clock signal that is synchronized with the clock signals that are tapped at other points in the integrated circuit. The time-delay circuits are configured so as to effect a prescribable time delay of the input signal with reference to an output signal. Conventional time delay circuits are, however, temperature-dependent. As a result, the respective signals experience a different time delay as a function of the ambient temperature and/or the junction temperature. The time-delay interval of the time delay circuits is influenced, in particular, during the heating of the integrated circuit as it is being used. Since a plurality of time delay circuits with different time-delay intervals are frequently provided, and since the signal transit times via line lengths are essentially not temperature-dependent, the result of this is that the signals become asynchronous relative to one another.
It is accordingly an object of the invention to provide an electronic circuit for generating an output voltage having a defined temperature dependence which overcomes the above-mentioned disadvantages of the prior art devices of this general type, and provides a time-delay circuit that makes a temperature-dependent time delay available in a simple way.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic circuit. The electronic circuit has a bandgap circuit for generating a defined temperature-constant voltage and a temperature-dependent current, and a conversion circuit connected to the bandgap circuit and generating an output voltage from the temperature-dependent current and the defined temperature-constant voltage. The output voltage has a defined temperature dependence.
According to the invention, the electronic circuit for generating the output voltage having the defined temperature dependence is provided. The electronic circuit has a bandgap circuit with the aid of which it is possible to generate a temperature-constant voltage and a temperature-dependent current having the defined temperature dependence. The electronic circuit also has the conversion circuit in order to generate the output voltage from the temperature-dependent current and the temperature-constant voltage. It is possible thereby to generate an output voltage having the defined temperature dependence that can be applied as a supply voltage to a time delay circuit in order to set the delay time.
The conversion circuit can preferably have a first resistor at whose first terminal the temperature-constant voltage is applied, and whose second terminal is connected to a first terminal of a second resistor. The second terminal of the second resistor is connected to a supply voltage potential. A first terminal of a third resistor is connected to the second terminal of the first resistor. The temperature-dependent current is supplied to a second terminal of the third resistor, in which it is possible to tap the output voltage at the second terminal of the third resistor.
Bandgap circuits are circuits that are frequently used in integrated circuits in order to generate temperature-constant voltages. The bandgap circuits can also be used for the purpose of generating a current with a defined temperature-dependence. The conversion circuit now provides for the temperature-dependent current to be converted into a temperature-dependent voltage with the aid of the third resistor, and for the voltage to be added to the temperature-constant voltage impressed via the second resistor. The output voltage can be set in a defined fashion by the suitable selection of the first, second and third resistors as well as given knowledge of the temperature dependence of the temperature-dependent current and the temperature-constant voltage. The output voltage can then be used, for example, as a supply voltage for a suitable time-delay circuit, as a result of which the temperature dependence of the time-delay circuit is compensated by the temperature dependence of the supply voltage.
It can be provided that the output voltage is connected to a high-resistance input of an amplifier circuit in order to decouple the output voltage from a subsequent low-resistance consumer such that substantially no current flows off from the second terminal of the third resistor during tapping of the amplified output voltage. In this way, the conversion circuit can be set more accurately to the desired temperature dependence of the output voltage, since an input resistance of a connected amplifier circuit or similar downstream circuit need not be known. It is therefore possible to set the temperature-dependent portion of the output voltage merely through knowledge of the temperature-dependent current and the resistance value of the third resistor.
It can be provided, furthermore, that the bandgap circuit has a first transistor whose first terminal is connected to a second supply voltage potential and whose second terminal is connected to a first terminal of a first diode. The second terminal of the first diode is connected to the first supply voltage potential. The bandgap circuit also has a second transistor, whose first terminal is connected to the second supply voltage potential and whose second terminal is connected to a first terminal of a fourth resistor. A second terminal of the fourth resistor is connected to a first terminal of a second diode, the second terminal of the second diode being connected to the first supply voltage potential. Present at the control inputs of the first transistor and the second transistor is a control voltage that depends on the voltage difference between the second terminal of the first transistor and the second terminal of the second transistor, such that the transistors connected to the control voltage are operated at one operating point.
Both a constant voltage and a temperature-dependent current can be generated with the aid of the control voltage thus generated, which has a prescribed temperature dependence. Provided for this purpose is, for example, a third transistor, whose first terminal is connected to the second supply voltage potential, and at whose second terminal it is possible to tap the temperature-dependent current. For this purpose, the temperature-dependent control voltage is applied at the control input of the third transistor. Since the third transistor is likewise operated at an operating point, the dependence of the current at the second terminal of the third transistor is substantially determined by the control voltage.
In order to-generate the constant voltage, a fourth transistor is provided whose first terminal is connected to the second supply voltage potential and whose second terminal is connected to the first terminal of a fifth resistor. A second terminal of the fifth resistor is connected to a first terminal of a third diode, a second terminal of the third diode being connected to the first supply voltage potential. A control input of the fourth transistor is connected to the temperature-dependent control voltage.
A fixed temperature-dependent current that effects a temperature-dependent voltage drop across the fifth resistor flows in a fashion controlled by the control voltage through the fourth transistor. Owing to the temperature dependence of the diode, which is likewise known, the voltages are added together via the third diode and via the fifth resistor. This also results in the setting for the control voltage and the temperature dependence thereof. The surface area ratio of the first diode to the second diode is selected such that there flows through the fourth transistor a specific current that generates a specific voltage drop in the fifth resistor. The voltage drop across the fifth resistor and the voltage drop across the third diode are necessarily temperature-dependent in opposite ways, and so the temperature dependences cancel one another out, that is to say the sum of the voltage drops across the fifth resistor and the third diode is substantially constant. A temperature-constant voltage can be tapped in this way at the first terminal of the fifth resistor.
The bandgap circuit according to the invention thus renders it possible to make available a temperature-constant voltage, and a current that is temperature-dependent in a defined fashion and is converted in an appropriate conversion circuit into an output voltage that is temperature-dependent in a defined fashion and has a predetermined temperature dependence.
In accordance with an added feature of the invention, the first diode and the second diode have identical temperature dependencies. The third diode has a temperature dependency of approximately xe2x88x922 mV/K.
In accordance with another feature of the invention, the fourth resistor and/or the fifth resistor has a temperature dependency.
In accordance with an additional feature of the invention, the first, second, third and/or fourth transistor is a field-effect transistor. The first, second and/or third diode is a bipolar transistor having a base terminal set at an equivalent potential as the second terminal of the diode.
In accordance with a further feature of the invention, the first diode and the second diode have active surfaces with a predetermined surface area ratio.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electronic circuit for generating an output voltage having a defined temperature dependence, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.